1. Field of Endeavor
The present invention relates to phosphoric acid fuel cells and more particularly to electro-mechanical systems phosphoric acid fuel cells.
2. State of Technology
U.S. Pat. No. 6,833,204 to Hiroyuki Oyanagi et al, assigned to Honda Giken Kogyo Kabushiki Kasha, issued Dec. 21, 2004; as well as U.S. Pat. No. 6,703,152 and United States Patent Applications Nos. 20040009377, 20020012823, and 20020012822; provide the following state of technology information: “The phosphoric acid fuel cell has a power-generating cell which is provided with an electrolyte-electrode assembly comprising an anode electrode, a cathode electrode, and an electrolyte layer interposed between the both electrodes. The electrolyte layer is generally constructed such that pores of a porous silicon carbide member is impregnated with concentrated phosphoric acid (liquid electrolyte). However, another type of the electrolyte layer is also known, in which a membrane of basic polymer such as polybenzimidazole is impregnated with phosphoric acid or sulfuric acid (see U.S. Pat. No. 5,525,436). In the phosphoric acid fuel cell, a predetermined number of the power-generating cells are electrically connected in series with each other to provide a fuel cell stack which is accommodated in a container. When the phosphoric acid fuel cell is operated, at first, the hydrogen-containing gas is supplied to the anode electrode, and the oxygen-containing gas is supplied to the cathode electrode.
The hydrogen in the hydrogen-containing gas is ionized on the anode electrode in a manner as represented by the following reaction formula (A). As a result, the hydrogen ion and the electron are generated.2H2→4H++4e   (A)The hydrogen ion is moved toward the cathode electrode via the electrolyte layer. On the other hand, the electron is extracted by an external circuit which is electrically connected to the anode electrode and the cathode electrode. The electron is utilized as the DC electric energy to energize the external circuit, and then it arrives at the cathode electrode. The hydrogen ion moved to the cathode electrode and the electron arrived at the cathode electrode via the external circuit cause the reaction as represented by the following reaction formula (B) together with the oxygen in the oxygen-containing gas supplied to the cathode electrode.O2+4H++4e→2H2O  (B)The reaction according to the reaction formula (B) is slow as compared with the reaction formula (A). That is, the reaction represented by the reaction formula (B) constitutes the rate-determining step in the overall cell reaction of the phosphoric acid fuel cell.”